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Resolving Ethernet Collisions


                                                                                        By GURU:  DAVE SMITH



Q: If you keep getting Ethernet collisions on your hub. And it seems to happen when you transfer large files, or print to network printer, or download from the Net. How can you isolate the cause of  the problem and resolve it?


A: A collision light on your hub will go off and your network will slow down when more than one device transmits on the same Ethernet channel simultaneously. The signals are said to "collide." For your hub, it's like trying to understand what's being said when two people are talking at the same time.


First, check to see if the network card has been manually set to "full-duplex." A telephone is a full-duplex device because both parties can talk at once. But a hub is a repeater and cannot support full duplex without frequent collisions.


To adjust the duplex setting of your network interface card in Windows, follow these steps:

Right click on Network Neighborhood, select Properties

Select your network adapter in the top window, then click on Properties

Select the Advanced tab

Under Property, select Duplex Mode

In the Value pull-down menu, select the desired mode


When surveying the computers in the TechTV office, we found that not all Windows machines allow you to do this. If you can't find these settings, refer to your network adapter's manual.


Crimped wires

Another possible cause is an improperly crimped cable. If pairs of wires are not matched correctly, cross-talking occurs between the transmit and receive wires, triggering a collision. Properly crimped wires also reduce repeat transmissions of unreadable packets, resulting in increased network speed.


It is very important that Ethernet cables are pinned correctly. When you look at the RJ-45 connector of a cable, with the clip facing away, pins one through eight are arranged from left to right.


Pins one and two must be matched and twisted around each other throughout the length of the cable. Pin one is white and orange; pin two is just orange.

Pins three and six must be matched in the same fashion as one and two. Pin three is white and green; pin six is green.

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The remaining pins are not used in 10MB and 100MB Ethernet cable. Pins four (blue) and five (white and blue) are generally a matched and twisted pair, along with seven (white and brown) and eight (brown).


If all else fails


If you are certain all of the above is correct, a network card on one of your devices (including your computer and the hub) could be bad. Although time-consuming, swapping Ethernet cards should help you find the culprit.













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